Number of letters in Roman numeral representation of n.

Terms

a(0) =1a(1) =2a(2) =3a(3) =2a(4) =1a(5) =2a(6) =3a(7) =4a(8) =2a(9) =1a(10) =2a(11) =3a(12) =4a(13) =3a(14) =2a(15) =3a(16) =4a(17) =5a(18) =3a(19) =2a(20) =3a(21) =4a(22) =5a(23) =4a(24) =3a(25) =4a(26) =5a(27) =6a(28) =4a(29) =3